The Correct answer is B.

Explanation

The sum of the positive odd integers less than 50 is 1+3+5+…+45+47+49, and the sum of the positive even integers less than or equal to 50 is 2+4+6+…+46+48+50. When the first sum is subtracted from the second, the terms can be regrouped to form (2-1)+(4-3)+…+(48-47)+(50-49) , which is just 1+1+1+…+1, where there are 25 ones. Therefore, the correct answer is 25.